[codex] Tighten feedback evidence templates

[Conalh]

Summary

• require evidence links and team/repo context in false-positive and missing-signal issue forms
• add a regression test that keeps feedback templates aligned with validation tracking
• note the evidence requirement in the team validation playbook
• create the missing GitHub labels used by the feedback forms: detector, false-positive, and new-signal

Scope

Only touch GitHub issue templates for false-positive and missing-signal reports, the team validation playbook docs, and a regression test for issue-template evidence fields.

Validation

• node --test test/issue-template.test.mjs
• npm test
• npm run build
• git diff --check
• local TaskBound review returned NONE for the PR scope